The present invention relates to coating compositions containing fluorocarbon resins, more specifically to such resins that are adapted for application by roll coating techniques and which need not include isophorone as a solvent.
The exceptional durability of coatings containing fluorocarbon resins has been long known, and such coatings have found wide use for exterior applications such as for architectural building components, e.g., aluminum extrusions and building panels. Examples of this type of coating are disclosed in U.S. Pat. No. 4,314,004 (Stoneberg).
Fluorocarbon containing coating compositions of this type are typically applied by either spraying or roll coating. Because of the divergent viscosity properties desired for these two application methods (compositions for spraying are preferably thixotropic, whereas compositions for roll coating are preferably newtonian), different solvent systems have been developed. For roll coating applications, fluorocarbon coating compositions conventionally contained substantial amounts of isophorone as a solvent. Compositions formulated for spraying are also characterized by higher evaporation rates than desired for roll coating (evaporation rate less than 70). Isophorone was considered unique in its ability to provide a combination of properties required for roll coating these compositions, including relatively low solvency at room temperature, better solvency at elevated temperatures for the sake of coalescing the resin particles, moderate evaporation rate, and appropriate surface tension and viscosity properties. However, eliminating isophorone solvent from fluorocarbon coatings is now considered a desirable objective due to the toxicity and objectionable odor of isophorone.
Coating compositions based on fluorocarbon resins without isophorone have been disclosed in the prior art, but these compositions are either not intended for roll coating applications or fall short of providing the desired combination of properties for roll coating. In U.S. Pat. No. 4,824,728 (Parsons) a list of solvents for the disclosed fluorocarbon containing coating composition does not include isophorone, and the composition is stated generally as being capable of application by spraying or roll coating. However, all of the examples in that patent are directed to sprayable coatings only, and the gist of the disclosure throughout the patent is to provide formulations that have characteristics of sprayable coatings (thixotropic rheology, evaporation rates higher than 70).
Japanese Kokoku 3-34783 (1991) (Kansai Paint K.K.) discloses that cyclohexanone may be substituted for isophorone as a solvent in a fluorocarbon containing coating composition. However, cyclohexanone is also an environmentally undesirable solvent and has an objectionable odor. Therefore, it would be desirable to avoid cyclohexanone as well.